The 2012 metal prices you used were the Tetra Tech long range metal prices, which were significantly lower then the spot prices at that time(FS spot prices were $ 3.69 and $ 1736). The FS shows how you can estimate the change to NPV from both exchange rate and metal price parameters separately. Then you add the differences to get a net change in NPV from the FS base case value. The effect on NPV by the change in exchange rate by my calcs more than offsets the drop in metal prices from the spot or base case values in 2012 but I don't see how that helps much until we see what happens to the RE numbers.